The present invention relates to an improvement in the process for preparing cyclotetramethylenetetranitramine, commonly and hereinafter referred to as HMX.
HMX is a powerful explosive of considerable military interest. The batch process currently practiced for the manufacture of HMX is a variation of the original Bachmann process consisting of the nitrolysis of hexamethylenetetramine, usually and hereinafter referred to as hexamine, with a mixture of nitric acid and ammonium nitrate in a medium of acetic acid and acetic anhydride. The batch nitration process is commonly divided into four parts or stages: a first addition of reagents followed by a first aging period; then a second addition of reagents followed by a second aging period. More specifically, the process is carried out by charging the reaction vessel with a mixture or "heel" of acetic acid and acetic anhydride to provide a stirrable liquid medium into which the reagents are introduced. The first addition of reagents is then made by concurrently and proportionately introducing separate streams of a solution of hexamine in glacial acetic acid, a solution of ammonium nitrate in conc. nitric acid, and acetic anhydride, after which the reaction mixture is agitated and permitted to age for several minutes. Thereafter, a second addition of reagents is made by concurrently and proportionately introducing separate streams of acetic anhydride and a solution of ammonium nitrate in conc. nitric acid, after which the reaction mixture is agitated and allowed to age for a substantial period. During these operations the temperature of the reaction mixture is usually maintained at about 40.degree.-45.degree. C. Following the second aging period the reaction mixture is diluted with water, which hydrolyzes any excess acetic anhydride and dilutes the acetic acid concentration to about 80 weight percent. The mixture is then heated to about 110.degree. C. to decompose undesirable by-products, such as linear nitramines, and then filtered to isolate the HMX product.